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Oxygen Isotopic Composition (oxygen + isotopic_composition)
Selected AbstractsCarbon and Oxygen Isotopic Composition of Surface-Sediment Carbonate in Bosten Lake (Xinjiang, China) and its Controlling FactorsACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 2 2009Chengjun ZHANG Abstract: Bosten Lake is a mid-latitude lake with water mainly supplied by melting ice and snow in the Tianshan Mountains. The depositional environment of the lake is spatially not uniform due to the proximity of the major inlet and the single outlet in the western part of the lake. The analytical results show that the carbon and oxygen isotopic composition of recent lake sediments is related to this specific lacustrine depositional environment and to the resulting carbonate mineralogy. In the southwestern lake region between the Kaidu River inlet and the Kongqi River outlet, carbon isotope composition (,13C) values of the carbonate sediment (,1, to ,2,) have no relation to the oxygen isotope composition of the carbonate (,18O) values (,7, to ,8,), with both isotopes showing a low variability. The carbonate content is low (<20%). Carbonate minerals analyzed by X-ray diffraction are mainly composed of calcite, while aragonite was not recorded. The salinity of the lake water is low in the estuary region as a result of the Kaidu River inflow. In comparison, the carbon and oxygen isotope values are higher in the middle and eastern parts of the lake, with ,13C values between approximately +0.5, and +3,, and ,18O values between ,1, and ,5,. There is a moderate correlation between the stable oxygen and carbon isotopes, with a coefficient of correlation r of approximately 0.63. This implies that the lake water has a relatively short residence time. Carbonate minerals constitute calcite and aragonite in the middle and eastern region of the lake. Aragonite and Mg,calcite are formed at higher lake water salinity and temperatures, and larger evaporation effects. More saline lake water in the middle and eastern region of the lake and the enhanced isotopic equilibrium between water and atmospheric CO2 cause the correlating carbon and oxygen isotope values determined for aragonite and Mg,calcite. Evaporation and biological processes are the main reasons for the salinity and carbonate mineralogy influence of the surface-sediment carbonate in Bosten Lake. The lake water residence time and the CO2 exchange between the atmosphere and the water body control the carbon and oxygen isotope composition of the carbonate sediment. In addition, organic matter pollution and decomposition result in the abnormally low carbon isotope values of the lake surface-sediment carbonate. [source] Geochemical constraints of the eclogite and granulite facies metamorphism as recognized in the Raobazhai complex from North Dabie Shan, ChinaJOURNAL OF METAMORPHIC GEOLOGY, Issue 1 2001Y. L. Xiao Abstract A combined study of major and trace elements, fluid inclusions and oxygen isotopes has been carried out on garnet pyroxenite from the Raobazhai complex in the North Dabie Terrane (NDT). Well-preserved compositional zoning with Na decreasing and Ca and Mg increasing from the core to rim of pyroxene in the garnet pyroxenite indicates eclogite facies metamorphism at the peak metamorphic stage and subsequent granulite facies metamorphism during uplift. A P,T path with substantial heating (from c. 750 to 900 °C) after the maximum pressure reveals a different uplift history compared with most other eclogites in the South Dabie Terrane (SDT). Fluid inclusion data can be correlated with the metamorphic grade: the fluid regime during the peak metamorphism (eclogite facies) was dominated by N2 -bearing NaCl-rich solutions, whereas it changed into CO2 -dominated fluids during the granulite facies retrograde metamorphism. At a late retrograde metamorphic stage, probably after amphibolite facies metamorphism, some external low-salinity fluids were involved. In situ UV-laser oxygen isotope analysis was undertaken on a 7 mm garnet, and impure pyroxene, amphibole and plagioclase. The nearly homogeneous oxygen isotopic composition (,18OVSMOW = c. 6.7,) in the garnet porphyroblast indicates closed fluid system conditions during garnet growth. However, isotopic fractionations between retrograde phases (amphibole and plagioclase) and garnet show an oxygen isotopic disequilibrium, indicating retrograde fluid,rock interactions. Unusual MORB-like rare earth element (REE) patterns for whole rock of the garnet pyroxenite contrast with most ultra-high-pressure (UHP) eclogites in the Dabie-Sulu area. However, the age-corrected initial ,Nd(t) is ,,2.9, which indicates that the protolith of the garnet pyroxenite was derived from an enriched mantle rather than from a MORB source. Combined with the present data of oxygen isotopic compositions and the characteristic N2 content in the fluid inclusions, we suggest that the protolith of the garnet pyroxenite from Raobazhai formed in an enriched mantle fragment, which has been exposed to the surface prior to the Triassic metamorphism. [source] Combined oxygen and silicon isotope analysis of biogenic silica,JOURNAL OF QUATERNARY SCIENCE, Issue 4 2008Melanie J. Leng Abstract There is increasing interest in the use of biogenic silica O and Si isotope ratios to understand climate and environmental processes. Virtually all of the fairly substantial body of literature deals with either oxygen or silicon. This is partly because measurement of oxygen isotope composition is done using either vacuum dehydration, isotope exchange or stepped fluorination techniques, while increasingly researchers are turning to multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS) for Si isotope analysis, even though Si isotope analysis can be done using fluorination methods used for the oxygen isotope measurements. Here we describe a procedure for simultaneous determination of isotopic abundances of oxygen and silicon from the same aliquot of biogenic silica. Pure silica is dissociated into O and Si compounds using a fluorination technique, in which reaction with bromine pentafluoride (BrF5) produces oxygen (O2, subsequently converted to CO2), silicon tetrafluoride (SiF4) and other fluorine by-products (e.g. BrF3). These compounds are cryogenically separated using cold traps. Yields for oxygen and silicon recovery are 70,80% for biogenic silica depending on the nature of the hydrous layer and 97,99% for pure quartz. Reproducibility of the oxygen isotopic composition is ca. 0.3, and silicon between 0.06,0.12,. © Natural Environment Research Council (NERC) copyright 2008. Reproduced with the permission of NERC. Published by John Wiley & Sons, Ltd. [source] A study of Mg and K isotopes in Allende CAIs: Implications to the time scale for the multiple heating processesMETEORITICS & PLANETARY SCIENCE, Issue 12 2006Motoo Ito The 7R-19,1 contains 16O-rich and 16O-poor melilite grains and define a single isochron corresponding to an initial 26Al/27Al ratio of (6.6 ± 1.3) × 10,5. The Al-Mg isochron, O isotope measurements and petrography of melilite in 7R-19,1 indicate that 16O-poor melilite crystallized within 0.4 Myr after crystallization of 16O-rich melilite, suggesting that oxygen isotopic composition of the CAI-forming region changed from 16O-rich to 16O-poor within this time interval. The 16O-poor melilite is highly depleted in K compared to the adjacent 16O-rich melilite, indicating evaporation during remelting of 7R-19,1. We determined the isochron for 41Ca- 41K isotopic systematics in EGG3 pyroxene with (4.1 ± 2.0) × 10,9 (2s,) as an initial ratio of 41Ca/40Ca, which is at least two times smaller than the previous result (Sahijipal et al. 2000). The ratio of 41Ca/40Ca in the EGG3 pyroxene grain agrees within error with the value obtained by Hutcheon et al. (1984). No evidence for the presence of 41K excess (decay product of a short-lived radionuclide 41Ca) was found in 7R-19,1 and HN3,1. We infer that the CAI had at least an order of magnitude lower than canonical 41Ca/40Ca ratio at the time of the CAI formation. [source] Ibitira: A basaltic achondrite from a distinct parent asteroid and implications for the Dawn missionMETEORITICS & PLANETARY SCIENCE, Issue 5 2005David W. MITTLEFEHLDT The mean Fe/Mn ratio of pyroxenes in Ibitira with <10 mole% wollastonite component is 36.4 ± 0.4; this value is well resolved from those of similar pyroxenes in five basaltic eucrites studied for comparison, which range from 31.2 to 32.2. Data for the latter five eucrites completely overlap. Ibitira pyroxenes have lower Fe/Mg than the basaltic eucrite pyroxenes; thus, the higher Fe/Mn ratio does not reflect a simple difference in oxidation state. Ibitira also has an oxygen isotopic composition, alkali element contents, and a Ti/Hf ratio that distinguish it from basaltic eucrites. These differences support derivation from a distinct parent asteroid. Thus, Ibitira is the first recognized representative of the fifth known asteroidal basaltic crust, the others being the HED, mesosiderite, angrite, and NWA 011 parent asteroids. 4 Vesta is generally assumed to be the HED parent asteroid. The Dawn mission will orbit 4 Vesta and will perform detailed mapping and mineralogical, compositional, and geophysical studies of the asteroid. Ibitira is only subtly different from eucritic basalts. A challenge for the Dawn mission will be to distinguish different basalt types on the surface and to attempt to determine whether 4 Vesta is indeed the HED parent asteroid. [source] Determining the possible building blocks of the Earth and MarsMETEORITICS & PLANETARY SCIENCE, Issue 5 2004Thomas H. Burbine Only a very small percentage of the combinations match the oxygen isotopic composition, the assumed bulk FeO concentration, and the assumed Fe/Al weight ratio for the Earth. Since chondrites are enriched in silicon relative to estimates of the bulk Earth, none of the combinations fall near the terrestrial magmatic fractionation trend line in Mg/Si-Al/Si space. More combinations match the oxygen isotopic composition and the assumed bulk FeO concentration for Mars. These combinations fall near the trend for shergottite meteorites in Mg/Si-Al/Si space. One explanation for the difficulty in forming Earth out of known chondrites is that the Earth may be composed predominately of material that did not survive to the present day as meteorites. Another explanation could be that significant amounts of silicon are sequestered in the core and/or lower mantle of the Earth. [source] Evaporative enrichment and time lags between ,18O of leaf water and organic pools in a pine standPLANT CELL & ENVIRONMENT, Issue 5 2007ROMAIN L. BARNARD ABSTRACT Understanding ecosystem water fluxes has gained increasing attention, as climate scenarios predict a drier environment for many parts of the world. Evaporative enrichment of 18O (,18O) of leaf water and subsequent enrichment of plant organic matter can be used to characterize environmental and physiological factors that control evaporation, based on a recently established mechanistic model. In a Pinus sylvestris forest, we measured the dynamics of oxygen isotopic composition (,18O) every 6 h for 4 d in atmospheric water vapour, xylem sap, leaf water and water-soluble organic matter in current (N) and previous year (N-1) needles, phloem sap, together with leaf gas exchange for pooled N and N-1 needles, and relevant micrometeorological variables. Leaf water ,18O showed strong diel periodicity, while ,18O in atmospheric water vapour and in xylem sap showed little variation. The ,18O was consistently lower for N than for N-1 needles, possibly related to phenological stage. Modelled leaf water ,18O showed good agreement with measured values when applying a non-steady state evaporative enrichment model including a Péclet effect. We determined the time lags between ,18O signals from leaf water to water-soluble foliar organic matter and to phloem sap at different locations down the trunk, which clearly demonstrated the relevance of considering these time-lag effects for carbon transport, source-sink and carbon flux partitioning studies. [source] Uncertainties in the oxygen isotopic composition of barium sulfate induced by coprecipitation of nitrateRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 19 2008Greg Michalski Coprecipitation of nitrate and sulfate by barium has probably resulted in significant error in numerous studies dealing with the oxygen isotopic composition of natural sulfates using chemical/thermal conversion of BaSO4 and analysis by isotope ratio mass spectrometry. In solutions where NO/SO molar ratios are above 2 the amount of nitrate coprecipitated with BaSO4 reaches a maximum of approximately 7% and decreases roughly linearly as the molar ratio decreases. The fraction of coprecipitated nitrate appears to increase with decreasing pH and is also affected by the nature of the cations in the precipitating solution. The size of the oxygen isotope artifact in sulfate depends both on the amount of coprecipitated nitrate and the ,18O and ,17O values of the nitrate, both of which can be highly variable. The oxygen isotopic composition of sulfate extracted from atmospheric aerosols or rain waters are probably severely biased because photochemical nitrate is usually also present and it is highly enriched in 18O (,18O ,50,90,) and has a large mass-independent isotopic composition (,17O ,20,32,). The sulfate ,18O error can be 2,5, with ,17O artifacts reaching as high as 4.0,. Copyright © 2008 John Wiley & Sons, Ltd. [source] A simple method for oxygen-18 determination of milligram quantities of water using NaHCO3 reagentRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 13 2003Akira Ijiri This paper presents a modified H2OCO2 equilibration method for stable oxygen isotopic composition (,18O) analysis of water. This method enables rapid and simple ,18O analysis of milligram quantities of water, by employing solid reagent NaHCO3 as the CO2 source, a small (0.6,mL) glass vial for the equilibration chamber, and an isotope-monitoring gas chromatography/mass spectrometry (irm-GC/MS) system for analysis. This method has several advantages, including simple handling for the H2OCO2 equilibration (without purging and/or evacuation treatments), rapid and easy ,18O analysis of equilibrated CO2, and highly sensitive and highly precise ,18O analysis of H2O, using samples as small as 10,mg and with a precision of less than ±0.12,. The time needed to attain oxygen isotopic equilibration between CO2 and water is also comparable (17,h for 10,mg H2O and 10,h for 100,mg H2O) to other previous methods using CO2 gas for the CO2 source. The extent of ,18O variation of sample water from its initial ,18O value due to isotope exchange with added NaHCO3 is also discussed. It is concluded that the correction needed is negligible (less than 0.1,) as long as the oxygen atom ratio () is less than 3.3,±,10,3 and provided the determination is made by comparing ,18O of CO2 equilibrated with sample water and that equilibrated with standard water of a moderately close ,18O value, less than 30, difference. Copyright © 2003 John Wiley & Sons, Ltd. [source] Compositional Variation of Hydrothermally Altered Volcanic Rocks in Hishikari Gold Epithermal System: A Useful Geochemical Indicator of Gold,Silver Epithermal MineralizationRESOURCE GEOLOGY, Issue 2 2010Naotatsu Shikazono Abstract The hydrothermally altered andesite hosting the Hishikari gold-silver vein deposits in southern Kyushu, Japan, is analyzed with respect to the spatial variation in chemical composition. The (CaO + Na2O) content is found to be inversely correlated with the K2O content as it progresses away from the site of mineralization. It was found that analytical data plotted on a (CaO + Na2O) , K2O diagram cannot be explained only by addition of K+ from the hydrothermal solution to the original rock and release of Ca2+ and Na+ from the original rock (K- alteration). Addition of Ca2+ and Na+ from the hydrothermal solution to the rock and release of K+ from the rock but release of K+, Ca2+, and Na+ to the hydrothermal solution (advanced argillic alteration) is important for causing the wide variations in K2O, CaO, and Na2O contents on the (CaO + Na2O) , K2O diagram. These variations can be explained by superimposed potassic, advanced argillic and calcium alterations. The altered rocks in the Honko-Sanjin area, Yamada area, and Masaki area analyzed by this study are characterized by their intermediate K2O content and variable CaO content, high K2O content and low CaO content, and low K2O content and low CaO content, respectively. The K2O, Na2O and CaO contents and oxygen isotopic composition of altered andesite, in conjunction with the solubility of gold as a thio complex, suggest that both gold deposition and the observed compositional variation of altered andesite are the result of mixing between acidic groundwater and neutral gold-bearing hydrothermal solution. The present results indicate that the compositional variation of hydrothermally altered rocks may represent a useful geochemical indicator of epithermal gold,silver mineralization. [source] Carbon and Oxygen Isotopic Composition of Surface-Sediment Carbonate in Bosten Lake (Xinjiang, China) and its Controlling FactorsACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 2 2009Chengjun ZHANG Abstract: Bosten Lake is a mid-latitude lake with water mainly supplied by melting ice and snow in the Tianshan Mountains. The depositional environment of the lake is spatially not uniform due to the proximity of the major inlet and the single outlet in the western part of the lake. The analytical results show that the carbon and oxygen isotopic composition of recent lake sediments is related to this specific lacustrine depositional environment and to the resulting carbonate mineralogy. In the southwestern lake region between the Kaidu River inlet and the Kongqi River outlet, carbon isotope composition (,13C) values of the carbonate sediment (,1, to ,2,) have no relation to the oxygen isotope composition of the carbonate (,18O) values (,7, to ,8,), with both isotopes showing a low variability. The carbonate content is low (<20%). Carbonate minerals analyzed by X-ray diffraction are mainly composed of calcite, while aragonite was not recorded. The salinity of the lake water is low in the estuary region as a result of the Kaidu River inflow. In comparison, the carbon and oxygen isotope values are higher in the middle and eastern parts of the lake, with ,13C values between approximately +0.5, and +3,, and ,18O values between ,1, and ,5,. There is a moderate correlation between the stable oxygen and carbon isotopes, with a coefficient of correlation r of approximately 0.63. This implies that the lake water has a relatively short residence time. Carbonate minerals constitute calcite and aragonite in the middle and eastern region of the lake. Aragonite and Mg,calcite are formed at higher lake water salinity and temperatures, and larger evaporation effects. More saline lake water in the middle and eastern region of the lake and the enhanced isotopic equilibrium between water and atmospheric CO2 cause the correlating carbon and oxygen isotope values determined for aragonite and Mg,calcite. Evaporation and biological processes are the main reasons for the salinity and carbonate mineralogy influence of the surface-sediment carbonate in Bosten Lake. The lake water residence time and the CO2 exchange between the atmosphere and the water body control the carbon and oxygen isotope composition of the carbonate sediment. In addition, organic matter pollution and decomposition result in the abnormally low carbon isotope values of the lake surface-sediment carbonate. [source] A look inside ,black box' hydrograph separation models: a study at the Hydrohill catchmentHYDROLOGICAL PROCESSES, Issue 10 2001Carol Kendall Abstract Runoff sources and dominant flowpaths are still poorly understood in most catchments; consequently, most hydrograph separations are essentially ,black box' models where only external information is used. The well-instrumented 490 m2 Hydrohill artificial grassland catchment located near Nanjing (China) was used to examine internal catchment processes. Since groundwater levels never reach the soil surface at this site, two physically distinct flowpaths can unambiguously be defined: surface and subsurface runoff. This study combines hydrometric, isotopic and geochemical approaches to investigating the relations between the chloride, silica, and oxygen isotopic compositions of subsurface waters and rainfall. During a 120 mm storm over a 24 h period in 1989, 55% of event water input infiltrated and added to soil water storage; the remainder ran off as infiltration-excess overland flow. Only about 3,5% of the pre-event water was displaced out of the catchment by in-storm rainfall. About 80% of the total flow was quickflow, and 10% of the total flow was pre-event water, mostly derived from saturated flow from deeper soils. Rain water with high ,18O values from the beginning of the storm appeared to be preferentially stored in shallow soils. Groundwater at the end of the storm shows a wide range of isotopic and chemical compositions, primarily reflecting the heterogeneous distribution of the new and mixed pore waters. High chloride and silica concentrations in quickflow runoff derived from event water indicate that these species are not suitable conservative tracers of either water sources or flowpaths in this catchment. Determining the proportion of event water alone does not constrain the possible hydrologic mechanisms sufficiently to distinguish subsurface and surface flowpaths uniquely, even in this highly controlled artificial catchment. We reconcile these findings with a perceptual model of stormflow sources and flowpaths that explicitly accounts for water, isotopic, and chemical mass balance. Copyright © 2001 John Wiley & Sons, Ltd. [source] Geochemical constraints of the eclogite and granulite facies metamorphism as recognized in the Raobazhai complex from North Dabie Shan, ChinaJOURNAL OF METAMORPHIC GEOLOGY, Issue 1 2001Y. L. Xiao Abstract A combined study of major and trace elements, fluid inclusions and oxygen isotopes has been carried out on garnet pyroxenite from the Raobazhai complex in the North Dabie Terrane (NDT). Well-preserved compositional zoning with Na decreasing and Ca and Mg increasing from the core to rim of pyroxene in the garnet pyroxenite indicates eclogite facies metamorphism at the peak metamorphic stage and subsequent granulite facies metamorphism during uplift. A P,T path with substantial heating (from c. 750 to 900 °C) after the maximum pressure reveals a different uplift history compared with most other eclogites in the South Dabie Terrane (SDT). Fluid inclusion data can be correlated with the metamorphic grade: the fluid regime during the peak metamorphism (eclogite facies) was dominated by N2 -bearing NaCl-rich solutions, whereas it changed into CO2 -dominated fluids during the granulite facies retrograde metamorphism. At a late retrograde metamorphic stage, probably after amphibolite facies metamorphism, some external low-salinity fluids were involved. In situ UV-laser oxygen isotope analysis was undertaken on a 7 mm garnet, and impure pyroxene, amphibole and plagioclase. The nearly homogeneous oxygen isotopic composition (,18OVSMOW = c. 6.7,) in the garnet porphyroblast indicates closed fluid system conditions during garnet growth. However, isotopic fractionations between retrograde phases (amphibole and plagioclase) and garnet show an oxygen isotopic disequilibrium, indicating retrograde fluid,rock interactions. Unusual MORB-like rare earth element (REE) patterns for whole rock of the garnet pyroxenite contrast with most ultra-high-pressure (UHP) eclogites in the Dabie-Sulu area. However, the age-corrected initial ,Nd(t) is ,,2.9, which indicates that the protolith of the garnet pyroxenite was derived from an enriched mantle rather than from a MORB source. Combined with the present data of oxygen isotopic compositions and the characteristic N2 content in the fluid inclusions, we suggest that the protolith of the garnet pyroxenite from Raobazhai formed in an enriched mantle fragment, which has been exposed to the surface prior to the Triassic metamorphism. [source] Oxygen isotope and 26Al- 26Mg systematics of aluminum-rich chondrules from unequilibrated enstatite chondritesMETEORITICS & PLANETARY SCIENCE, Issue 1 2006Yunbin Guan Among eleven aluminum-rich chondrules and two plagioclase fragments measured for 26Al- 26Mg systematics, only one aluminum-rich chondrule contains excess 26Mg from the in situ decay of 26Al; the inferred initial ratio (26Al/27Al)o = (6.8 ± 2.4) × 10,6 is consistent with ratios observed in chondrules from carbonaceous chondrites and unequilibrated ordinary chondrites. The oxygen isotopic compositions of five aluminum-rich chondrules and one plagioclase fragment define a line of slope ,0.6 ± 0.1 on a three-oxygen-isotope diagram, overlapping the field defined by ferromagnesian chondrules in enstatite chondrites but extending to more 16O-rich compositions with a range in ,18O of about ,12,. Based on their oxygen isotopic compositions, aluminum-rich chondrules in unequilibrated enstatite chondrites are probably genetically related to ferromagnesian chondrules and are not simple mixtures of materials from ferromagnesian chondrules and calcium-aluminum-rich inclusions (CAIs). Relative to their counterparts from unequilibrated ordinary chondrites, aluminum-rich chondrules from unequilibrated enstatite chondrites show a narrower oxygen isotopic range and much less resolvable excess 26Mg from the in situ decay of 26Al, probably resulting from higher degrees of equilibration and isotopic exchange during post-crystallization metamorphism. However, the presence of 26Al-bearing chondrules within the primitive ordinary, carbonaceous, and now enstatite chondrites suggests that 26Al was at least approximately homogeneously distributed across the chondrite-forming region. [source] Northwest Africa 011: A "eucritic" basalt from a non-eucrite parent bodyMETEORITICS & PLANETARY SCIENCE, Issue 3 2005Christine Floss This meteorite bears many similarities to the eucrites it was initially identified with, although oxygen isotopic compositions rule out a genetic relationship. Like many eucrites, NWA 011 crystallized from a source with approximately chondritic proportions of REE, although a slightly LREE-enriched bulk composition with a small positive Eu anomaly, as well as highly fractionated Fe/Mg ratios and depleted Sc abundances (Korotchantseva et al. 2003), suggest that the NWA 011 source experienced some pyroxene and/or olivine fractionation. Thermal metamorphism resulted in homogenization of REE abundances within grains, but NWA 011 did not experience the intergrain REE redistribution seen in some highly metamorphosed eucrites. Despite a similarity in oxygen isotopic compositions, NWA 011 does not represent a basaltic partial melt from the acapulcoite/lodranite parent body. The material from which NWA 011 originated may have been like some CH or CB chondrites, members of the CR chondrite clan, which are all related through oxygen isotopic compositions. The NWA 011 parent body is probably of asteroidal origin, possibly the basaltic asteroid 1459 Magnya. [source] ,18O of water vapour, evapotranspiration and the sites of leaf water evaporation in a soybean canopyPLANT CELL & ENVIRONMENT, Issue 9 2008LISA R. WELP ABSTRACT Stable isotopes in water have the potential to diagnose changes in the earth's hydrological budget in response to climate change and land use change. However, there have been few measurements in the vapour phase. Here, we present high-frequency measurements of oxygen isotopic compositions of water vapour (,v) and evapotranspiration (,ET) above a soybean canopy using the tunable diode laser (TDL) technique for the entire 2006 growing season in Minnesota, USA. We observed a large variability in surface ,v from the daily to the seasonal timescales, largely explained by Rayleigh processes, but also influenced by vertical atmospheric mixing, local evapotranspiration (ET) and dew formation. We used ,ET measurements to calculate the isotopic composition at the sites of evaporative enrichment in leaves (,L,e) and compared that with the commonly used steady-state prediction (,L,s). There was generally a good agreement averaged over the season, but larger differences on individual days. We also found that vertical variability in relative humidity and temperature associated with canopy structure must be addressed in canopy-scale leaf water models. Finally, we explored this data set for direct evidence of the Péclet effect. [source] Tracing the geographical origin of beefs being circulated in Korean markets based on stable isotopesRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 1 2010Yeon-Sik Bong We have examined the carbon, nitrogen and oxygen isotopic compositions of American, Mexican, Australian, New Zealand and Korean beefs, which are currently being circulated in Korean markets, to check whether stable isotope ratios can identify their country of origin. Each beef exhibited statistically distinct isotopic compositions, especially in oxygen and carbon, because of the different isotopic compositions of their water and cattle feeds. Nevertheless, their isotopic compositions still showed some overlap, especially among USA, Australian, and Korean beefs, which sometimes resulted in significant misidentification when a single isotope was considered. However, the discrimination was generally successful when both the carbon and the oxygen isotopes were used. Copyright © 2009 John Wiley & Sons, Ltd. [source] Stable carbon and oxygen isotopic determination of sub-microgram quantities of CaCO3 to analyze individual foraminiferal shellsRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 23 2004Toyoho Ishimura We have developed an analytical system to determine stable isotopic compositions (,13C and ,18O) of sub-microgram quantities of CaCO3 for the purpose of analyzing individual foraminiferal shells, using continuous-flow isotope ratio mass spectrometry (CF-IRMS). The system consists of a micro-volume CaCO3 decomposition tube, stainless steel CO2 purification vacuum line with a quantity-regulating unit, helium-purged CO2 purification line, gas chromatograph, and a CF-IRMS system. By using this system, we can determine stable carbon and oxygen isotopic compositions as low as 0.2,,g of CaCO3, with standard deviations of ±0.10, for ,13C and ±0.18, for ,18O within a 4-h reaction time and 30-min analysis period. Copyright © 2004 John Wiley & Sons, Ltd. [source] REE, Mn, Fe, Mg and C, O Isotopic Geochemistry of Calcites from Furong Tin Deposit, South China: Evidence for the Genesis of the Hydrothermal Ore-forming FluidsRESOURCE GEOLOGY, Issue 1 2010Yan Shuang Abstract The Furong tin deposit in the central Nanling region, South China, consists of three main types of mineralization ores, i.e. skarn-, altered granite- and greisen-type ores, hosted in Carboniferous and Permian strata and Mesozoic granitic intrusions. Calcite is the dominant gangue mineral intergrown with ore bodies in the orefield. We have carried out REE, Mn, Fe, and Mg geochemical and C, and O isotopic studies on calcites to constrain the source and evolution of the ore-forming fluids. The calcites from the Furong deposit exhibit middle negative Eu anomaly (Eu/Eu*= 0.311,0.921), except for one which has an Eu/Eu* of 1.10, with the total REE content of 5.49,133 ppm. The results show that the calcites are characterized by two types of REE distribution patterns: a LREE-enriched pattern and a flat REE pattern. The LREE-enriched pattern of calcites accompanying greisen-type ore and skarn-type ore are similar to those of Qitianling granite. The REE, Mn, Fe, and Mg abundances of calcites exhibit a decreasing tendency from granite rock mass to wall rock, i.e. these abundances of calcites associated with altered granite-type and greisen-type ores are higher than those associated with skarn-type ores. The calcites from primary ores in the Furong deposit show large variation in carbon and oxygen isotopic compositions. The ,13C and ,18O of calcites are ,0.4 to ,12.7, and 2.8 to 16.4,, respectively, and mainly fall within the range between mantle or magmatic carbon and marine carbonate. The calcites from greisen and altered granite ores in the Furong deposit display a negative correlation in the diagram of ,13C versus ,18O, probably owing to the CO2 -degassing of the ore-forming fluids. From the intrusion to wall-rock, the calcites display an increasing tendency with respect to ,13C values. This implies that the carbon isotopic compositions of the ore-bearing fluids have progressively changed from domination by magmatic carbon to sedimentary carbonate carbon. In combination with other geological and geochemical data, we suggest that the ore-forming fluids represent magmatic origin. We believe that the fluids exsolved from fractionation of the granitic magma, accompanying magmatism of the Qitianling granite complex, were involved in the mineralization of the Furong tin polymetallic deposit. [source] Chemical, Isotopic, and Fluid Inclusion Evidence for the Hydrothermal Alteration of the Footwall Rocks of the BIF-Hosted Iron Ore Deposits in the Hamersley District, Western AustraliaRESOURCE GEOLOGY, Issue 2 2003Makoto Haruna Abstract. The petrography, chemical, fluid inclusion and isotope analyses (O, Rb-Sr) were conducted for the shale samples of the Mount McRae Shale collected from the Tom Price, Newman, and Paraburdoo mines in the Hamersley Basin, Western Australia. The Mount McRae Shale at these mines occurs as a footwall unit of the secondary, hematite-rich iron ores derived from the Brockman Iron Formation, one of the largest banded iron formations (BIFs) in the world. Unusually low contents of Na, Ca, and Sr in the shales suggest that these elements were leached away from the shale after deposition. The ,18O (SMOW) values fall in the range of + 15.0 to +17.9 per mil and show the positive correlation with calculated quartz/sericite ratios of the shale samples. This suggests that the oxygen isotopic compositions of shale samples were homogenized and equilibrated by postdepositional event. The pyrite nodules hosted by shales are often rimmed by thin layers of silica of varying crystallinity. Fluid inclusions in quartz crystals rimming a pyrite nodule show homogenization temperatures ranging from 100 to 240d,C for 47 inclusions and salinities ranging from 0.4 to 12.3 wt% NaCl equivalent for 18 inclusions. These fluid inclusion data give direct evidence for the hydrothermal activity and are comparable to those of the vein quartz collected from the BIF-derived secondary iron ores (Taylor et al, 2001). The Rb-Sr age for the Mount McRae Shale is 1,952 ± 289 Ma and at least 200 million years younger than the depositional age of the Brockman Iron Formation of , 2.5 Ga in age. All the data obtained in this study are consistent with the suggestion that high temperature hydrothermal fluids were responsible for both the secondary iron ore formation and the alteration of the Mount McRae Shale. [source] | ||||||||||